The materials used for electrical and electronic components, such as connectors, springs, relays, contacts and switches, are required to possess high strength and good spring characteristics. High strength copper based alloys are currently used, with the most widely used copper based alloys being phosphor bronzes (CDA 510, CDA 511), and beryllium copper alloys (CDA 172, CDA 175).
Since phosphor bronzes contain a relatively high content (5 wt/%) of tin, the manufacturing process is difficult due to the segregation of tin during solidification. In addition, the cost of phosphor bronzes is higher due to the high content of expensive tin elements, in addition to the complex manufacturing processes.
Segregation of the tin element should be minimized during solidification, and the rolling conditions should be carefully controlled to avoid cracking during the thermomechanical processing. However, the mechanical properties of phosphor bronze (CDA 510) are inferior to those of beryllium copper alloys for electrical component applications.
Although beryllium copper alloys possess excellent mechanical properties with good electrical and thermal conductivity, the cost of these alloys is very high due to the beryllium content. Also, the use of beryllium alloys may create a health hazard problem when used, as the presence of beryllium requires that adequate safety precautions be mandatory for all melting, grinding, machining and welding operations.
A prior art copper alloy is disclosed in the specification of Japanese Patent Application No. SHO 52-5219 to Kokai. However, this particular alloy does not demonstrate an increase in tensile strength and ductility. A second prior art copper alloy is disclosed in the specification of Japanese Patent Application No. SHO 60-59035 to Kokai. This alloy demonstrates increased tensile strength, but requires the addition of phosphorus. Finally, a third prior art copper alloy is disclosed in the specification of Japanese Patent Application No. SHO 59-25935 to Kokai. This alloy possesses higher wear-resistant properties, rather than increased tensile strength, but requires the use of zinc, zirconium and iron additives.
The purpose of the instant invention is to develop a new low-cost, high performance, copper alloy possessing high strength and spring properties, but without requiring the use of expensive alloy elements. Advantageously, through use of the instant invention, the use of expensive alloy elements such as tin and beryllium is completely eliminated. Instead, large amounts of inexpensive alloy elements, such as zinc and aluminum, are added as major alloy elements to reduce cost. Also, small amounts of microalloy elements, such as silicon and zirconium (below 1%) are added for grain size refinement. Significantly, optimum thermomechanical manufacturing methods are employed to obtain excellent strength and ductility by grain size refinement and excellent spring characteristics are obtained by applying suitable heat treatment.
When utilizing the instant invention for the production of strip or sheet products, cold-rolling is employed. To make cold-rolling possible, the use of a face-centered-cubic (FCC) structure for the base matrix is desirable. In order to enhance the strength of the final product, several solid solution hardening elements can be added to the FCC matrix without forming a second phase, such as a body-centered-cubic (BCC) phase in the copper-zinc system. A very high strength can be obtained by superimposing various strengthening mechanisms such as grain size refinement, cold-rolling, and solid solution hardenings. Good spring characteristics can be achieved by a stress relief heat-treatment after a final cold-rolling process.